This is a competing renewal application to support our ongoing work to explore the function of neurofibromin in the cardiovascular system. Neurofibromin is encoded by the NF1 gene, which is mutated in von Recklinghausen Neurofibromatosis, a common genetic disorder characterized by benign and malignant tumors. Based in part upon our prior work funded by this grant, there is an increasing awareness of widespread cardiovascular complications of this disease, including congenital heart disease, hypertension and vascular anomalies. Nf1 knockout mice are embryonic lethal and display severe cardiac abnormalities. We have shown that these defects are related to a previously unrecognized function for neurofibromin in endothelial cells, including those that transform into mesenchyme to form the cardiac valves. More recently, we have also demonstrated important functions for neurofibromin in vascular smooth muscle, and preliminary data presented in this application demonstrate a myocyte-specific role in modulating cardiac hypertrophy. Neurofibromin can function as a Ras GAP to down-regulated Ras activity, but alternative intracellular signaling pathways have also been implicated. Many aspects of Nf1 loss of function are recapitulated in mice and humans by activating mutations in Shp2, a protein phosphatase that modulates diverse intracellular signaling pathways and which is mutated in Noonan syndrome. We propose to continue our elucidation of Nf1 function in the cardiovascular system by using in vivo and ex vivo analysis of cardiac valve development in the embryo to identify interactions between Nf1 and Shp2 and to identify downstream regulated pathways. We will then extend these findings to elucidate adult cardiovascular physiology. We will examine the role of neurofibromin in angiogenesis and endothelial function, using tissue specific knockout and rescued mice. Finally, we will elucidate the role of Nf1 and Shp2 in cardiac hypertrophy and heart failure using mouse models, including epistasis analysis, and we will identify parallel signaling pathways modulated by Nf1 and Shp2 in the embryo and in the adult heart. These approaches will have relevance not only to the development of effective therapies for Neurofibromatosis and Noonan syndrome, but also for a better understanding of signaling pathways regulating specific aspects of cardiovascular pathology. PUBLIC HEALTH RELEVANCE: This is a competing renewal request for a project focused on identifying the role of Nf1 in cardiovascular development and function. Our lab has shown that the gene causing Neurofibromatosis, Nf1, functions in vascular endothelium and smooth muscle;and preliminary data indicates that Nf1 is important in cardiac myocytes as well. We propose experiments to elucidate the mechanism of Nf1 function in the cardiovascular system with implications for the treatment of cardiovascular disorders in Neurofibromatosis, and for understanding of common diseases such as hypertension and heart failure.